Books, newspapers, brochures or other products to be printed are produced by means of different printing processes. The production of such printed products can be carried out, firstly, by conventional printing processes, such as planographic, relief, gravure or screen printing and, secondly, by digital processes, such as the computer-to-plate (CTP) technique. In the case of offset printing, the printed products are produced by using printing forms. In this case, the image or the text to be printed is transferred to printing form blanks—also called printing plates. In this case, a light-sensitive layer applied to a metal or plastic plate, based on silver or made of a photopolymer, is exposed by means of UV radiation. In addition, in particular in the area of the CTP technique, thermal plates are also used, on which an image can be set by the action of specific temperatures. Lasers are suitable both for exposing photosensitive plates and for setting images thermally. The size of the printing plate to be produced depends on the object to be printed. For all the processes in printing technology, an extremely wide range of plate formats belong to the prior art. In the area of the CTP technique, a series of systems for setting images on printing plates with an extremely wide range of formats have been known for a long time, such as the Laserstepper from Misomex, the Laserstar from Krause or Xpose! from the Lüscher company.
In printing technology, time is a key component. Automation of the production of printing plates is therefore a logical consequence. This is because fully automatic printing plate production as one operation in the entire printing process accelerates the throughput and increases the productivity of a print shop.
DE-A 40 38 544 describes an apparatus for producing printing plates. In this case, the plate blanks are arranged in stacks on stack carriers inside a magazine. This magazine contains a circulating conveyor constructed as a paternoster and driven, having a plurality of stack carriers arranged one behind another. The stack carriers can be removed from the magazine in the horizontal direction by means of a displacement device and can be conveyed onto the copying table by a holding or feeding apparatus. This feeding apparatus comprises a suction frame with suckers. The suction frame can be moved in the horizontal and vertical plane and, can transfer a plate blank to a copying table. The disadvantage with this apparatus is, in particular, the complicated elevator mechanism within the magazine.
The apparatus described in DE-C1 41 05 269 for loading and unloading printing plates is less complicated than the apparatus described previously. Here, the plate blanks, likewise mounted in cassettes, are stacked in the manner of a tower as a magazine. The individual plate blanks can be transferred from a desired cassette to the copying table by means of a feeding apparatus. For this purpose, the cassettes can be moved in the horizontal plane out of the magazine, so that the feeding apparatus can have access to the individual plate blanks. Not every cassette can be moved individually out of the tower; instead in each case the part of the tower is moved out, so that the desired cassette with the printing plates is arranged at the top. The feeding apparatus in turn comprises a rotary star, to whose projecting pivoting arms suction heads are fixed.
The disadvantage with the apparatuses described in DE-A 40 38 544 and DE-C 41 05 269 is that they are not capable of loading cylindrical drum exposers.
EP-A 0822 453 describes an apparatus and a method for picking up and transporting printing plates into an automated exposure device. A large number of printing plates is stored in the form of stacks in cassettes or magazines. Here, different magazines can contain different plate formats. The plate removal described in the application is carried out by a feeding apparatus. For this purpose, the desired plate formats are arranged by means of a complex elevator mechanism such that they can be reached by the feeding apparatus. The feeding apparatus comprises a horizontally arranged and horizontally displaceable plate with suction heads, by means of which heads the plate on which an image is to be set can be picked up by vacuum. The disadvantage with this apparatus is, in particular, the complicated elevator mechanism. In addition, this application does not provide any solution as to how the planar printing plate can ultimately be put into the cylindrical drum exposure by the feeding apparatus, on which it is arranged by means of vacuum, as described.
An apparatus for loading drum exposers is disclosed by EP-A 0887 181. In this case, a printing plate which is arranged in a planar fashion by means of vacuum on a feeding apparatus is inserted into a cylindrical drum exposer with the aid of a loading device. The printing plate is transferred from the feeding apparatus to the loading device via rotating rolls. The loading apparatus in turn moves over rails along the inner surface of the drum exposer, carrying the printing plate with it. The same loading device can move in the opposite direction and, as a result, can transfer a printing plate on which an image has already been set out of the drum exposer to a developing machine arranged downstream. The disadvantage with this device is its complexity. Firstly, there must be a roll system to remove the printing plate from the feeding apparatus and, secondly, specific rail systems have to be arranged on a drum exposer so that the loading device can move along the internal drum. In addition, this apparatus is suitable only for loading internal drum exposers.
The prior art likewise includes apparatuses for printing plate loading and unloading which can be obtained on the market, such as the plate loading system (PHS) relating to the “Xpose!” CTP exposer from the Lüscher company. In this apparatus, the printing plates are stored in a planar fashion and in stacks in cassettes. These cassettes are arranged on one another and can be moved out of the front side in the horizontal direction. The feeding apparatus comprises a cylinder and a device for positioning the cylinder. The cylinder is mounted on the positioning device such that it can be rotated with respect to its longitudinal axis. Arranged on the cylinder are suction heads which are connected to a vacuum system. By means of the positioning device, the cylinder can be moved both in the vertical and in the horizontal direction. In order to pick up a printing plate, a cassette is pushed horizontally out of the cassette stack and the cylinder is lowered vertically onto the printing plate until the suction heads make contact with the printing plate. The cylinder is rotated over the printing plate by means of a horizontal movement of the positioning device with the vacuum switched on, as a result of which the topmost printing plate of a cassette is firmly held on the outside of the cylinder as the cylinder rotates. By means of the vertical drive of the positioning device, the cylinder is drawn upward, together with the printing plate. The cylinder with the printing plate which has been picked up is then moved over the drum of the exposer by means of a horizontal displacement by the positioning device. Using the vertical drive of the positioning device, the cylinder with the printing plate is positioned on the inside of the drum, and the printing plate is inserted into the drum by switching off the vacuum. In order to remove the printing plate on which an image has been set, the same sequence of movements is carried out in the opposite order, with the difference that the printing plate is not put back again into the cassette from which it was removed but is placed in or on a carrier, which can be arranged instead of a cassette. This carrier is then connected to a developing device. The apparatus described is also capable of removing intermediate papers, which are located between the individual printing plates in order to protect the side on which an image is to be set, by means of the same mechanism described above. This can be done, for example, while a printing plate is having an image set on it. The disadvantage with this apparatus is its complexity. Firstly, a cylinder that can be rotated about its axis and has suction heads is needed. Secondly, a device which can be moved both in the vertical and in the horizontal direction is needed to position the cylinder. In addition, the size of the apparatus is disadvantageous.